From: Yury Norov <yury.norov@gmail.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
agk@redhat.com, snitzer@kernel.org, dm-devel@redhat.com,
vneethv@linux.ibm.com, oberpar@linux.ibm.com, hca@linux.ibm.com,
gor@linux.ibm.com, agordeev@linux.ibm.com,
borntraeger@linux.ibm.com, svens@linux.ibm.com,
almaz.alexandrovich@paragon-software.com,
linux@rasmusvillemoes.dk, linux-s390@vger.kernel.org,
ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org,
kernel-janitors@vger.kernel.org
Subject: Re: [PATCH 3/4] bitmap: Introduce bitmap_size()
Date: Sun, 3 Jul 2022 12:13:08 -0700 [thread overview]
Message-ID: <YsHqRDfCQVwyA2m1@yury-laptop> (raw)
In-Reply-To: <YsGz1Xp0RDM5ZhVY@smile.fi.intel.com>
On Sun, Jul 03, 2022 at 06:20:53PM +0300, Andy Shevchenko wrote:
> On Sun, Jul 03, 2022 at 08:50:19AM +0200, Christophe JAILLET wrote:
> > Le 02/07/2022 à 23:09, Yury Norov a écrit :
> > > On Sat, Jul 02, 2022 at 08:29:36PM +0200, Christophe JAILLET wrote:
>
> ...
>
> > > This should be dropped, for sure, and kmalloc() at line 128 should be
> > > replaced with bitmap_alloc().
> >
> > This kmalloc() is for a structure and a flexible array.
> >
> > You mean re-arranging the code to allocate the structure alone at first,
> > then the bitmap?
We can change struct primes to:
struct primes {
struct rcu_head rcu;
unsigned long last, sz;
unsigned long *primes;
};
And then either allocate twice:
new = kmalloc(sizeof(struct primes);
new->primes = bitmap_alloc(sz);
Or keep the same struct primes for all expansions, and just allocate
new bitmap for ->primes when needed. This is what I meant.
This a bit deeper rework, but it addresses Andy's concern about excessive
fragmentation. (Did anyone before complain? Is it measurable?)
> It's one way, but it will increase fragmentation of memory. The other one
> as it seems to me is to name a new API properly, i.e. bitmap_size_to_bytes().
>
> In such case you won't need renames to begin with. And then would be able
> to convert driver-by-driver in cases of duplicated code.
>
> I think that's what confused Yuri and I kinda agree that bitmap_size() should
> return bits, and not bytes. Also argument for pure bitmap_size() would be
> bitmap itself, but we have no way to detect the length of bitmap because we
> are using POD and not a specific data structure for it.
bitmap_size_to_bytes() sounds better. How many places in the kernel
do we have where we can't simply use bitmap_alloc(), and need this
machinery? If this is the only one, I'd prefer to switch it to
bitmap_alloc() instead.
Thanks,
Yury
next prev parent reply other threads:[~2022-07-03 19:13 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-02 18:28 [PATCH 0/4] Introduce bitmap_size() Christophe JAILLET
2022-07-02 18:29 ` [PATCH 1/4] s390/cio: Rename bitmap_size() as idset_bitmap_size() Christophe JAILLET
2022-07-02 18:54 ` Andy Shevchenko
2022-07-02 19:24 ` Christophe JAILLET
2022-07-02 19:32 ` Andy Shevchenko
2022-07-02 19:42 ` Christophe JAILLET
2022-07-02 20:46 ` Yury Norov
2022-07-04 4:28 ` Vineeth Vijayan
2022-07-02 18:29 ` [PATCH 2/4] fs/ntfs3: Rename bitmap_size() as ntfs3_bitmap_size() Christophe JAILLET
2022-07-02 18:58 ` Andy Shevchenko
2022-07-02 19:37 ` Christophe JAILLET
2022-07-02 20:57 ` Yury Norov
2022-07-02 18:29 ` [PATCH 3/4] bitmap: Introduce bitmap_size() Christophe JAILLET
2022-07-02 18:59 ` Andy Shevchenko
2022-07-02 21:09 ` Yury Norov
2022-07-03 6:50 ` Christophe JAILLET
2022-07-03 15:20 ` Andy Shevchenko
2022-07-03 19:13 ` Yury Norov [this message]
2022-07-03 20:41 ` Christophe JAILLET
2022-07-02 18:29 ` [PATCH 4/4] bitmap: Use bitmap_size() Christophe JAILLET
2022-07-02 20:44 ` [PATCH 0/4] Introduce bitmap_size() Yury Norov
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